CEC Abstracts in PDF format (as of 7/3/07) - CEC-ICMC 2013

CEC 2007 - Abstracts
Double-inlet is a key factor for a double-inlet type pulse tube
refrigerators. It is important to understand the characters of doubleinlet.
Deep research on characters of double-inlet will be very helpful
to reveal the mechanics of pulse tube refrigerator.
This work is supported by Natural Sciences Foundation of China
(50206025).
C1-D-03 Experimental Studies on a Two-Stage Pulse
Tube Cryocooler Reaching 3.3 K
S. Kasthurirengan, G. Srinivasa, G.S. Karthik, Centre
for Cryogenic Technology, Dept. of Physics, Indian
Institute of Science; K.P. Ramesh, Dept. of Physics,
Indian Institute of Science; K.A. Shafi, TKM College
of Engineering, Kollam, Kerala, India.
A two stage Pulse Tube Cryocooler is designed and fabricated, which
reaches no load temperatures of 3.3 K in the second stage and ~60 K
in the first stage respectively. The system provides a refrigeration
power of ~ 250mW at 5 K in the second stage. Stainless steel meshes
(size 200) and lead (Pb) granules are used as first stage regenerator
materials and combinations of Pb with Er3Ni or Pb with HoCu2 are
used as second stage regenerator materials. The system operates at 1.8
Hz using an indigenous rotary valve along with a 6 kW water-cooled
Helium compressor.
Studies conducted by varying the dimensions of Pulse Tubes and
regenerators for the first and second stages show that pulse tube
dimensions are more critical to the performance of the Cryocooler
than those of the regenerators. Experimental studies show that the
optimum volume ratio of Pb to Er3Ni or HoCu2 (in the second stage)
should be ~ 3:2 for the best performance of the Cryocooler. Further,
systems with HoCu2 performed better than those with Er3Ni. Pulse
Tube Cryocoolers performed better when operated with anti-parallel
double inlet valves than when operated with other DC flow
arrangements.
Theoretical analysis of the above two-stage Pulse Tube Cryocooler
system has been carried out using a simple isothermal model. The
experimentally measured cooling powers are in close agreement with
the theoretical predictions.
Financial support for the study has come from the Council of
Scientific and Industrial Research, New Delhi, India.
C1-D-04 A buffered rotary valve system of GM-type
pulse tube refrigerator
G. Hwang, J. Jung, S. Jeong, KAIST.
In a GM or a GM-type PTR (Pulse Tube Refrigerator), considerable
amount of helium flow is produced during the pressure transition
periods from high to low values or vice versa. In a conventional rotary
valve system, however, this kind of helium in- and out-flow which are
supplied directly from the helium compressor does not contribute to
the actual refrigeration power. We devised a buffered rotary valve
system in order to reduce such an unnecessary helium flow from the
compressor. In a buffered rotary valve system, pressurizing and
depressurizing flow is not solely supplied by the compressor but also
provided by a buffer volume. Theoretically, half of the transition flow
can be alleviated in the compressor with a single buffer. The aim of
the buffered rotary valve system is to use a compressor more
effectively and make the expansion process in PTR more efficient. In
this paper, the buffered rotary valve system is introduced at the first
time, fully described with simple thermodynamic analysis, and also
investigated experimentally to show its performance increase.
This research was supported by a grant from Center for Applied
Superconductivity Technology of the 21st Century Frontier R&D
Program funded by the Ministry of Science and Technology, Republic
of Korea.
C1-D-05 An experimental study of the G-M type two-
Stage Pulse Tube Cryocooler for cryopump
S.J. Park, Y.J. Hong, H.B. Kim, Korea Institute of
Machinery & Materials; S.J. Lee, Hyunmin
Laboratory.
The pulse tube cryocooler, which has no moving parts at its cold
section, is attractive in obtaining higher reliability, simpler
construction, and lower vibration than any other small cryocoolers.
Korea Institute of Machinery & Materials(KIMM) has developed G-
M type and Stirling type pulse tube cryocooler since 1992. The
developments in KIMM on the pulse tube cryocooler systems have
focused primarily on refrigeration capacity, efficiency and
performance reliability as well as mechanical reliability. The purpose
of this study is to provide reliable, efficient and long life cryocoolers
for cooling systems in cryopump and other applications. The G-M
type two-stage pulse tube cryocooler consists of a helium compressor,
a pulse tube, regenerator, orifice, double inlet valve, a buffer
(reservoir) volume and vacuum chamber. This paper describes the
two-stage pulse tube cryocoolers designed for cooling arrays of the
cryopump and their performance characteristics.
C1-D-06 Optimization of two stage pulse tube
refrigerator for the integrated current lead system
R. Maekawa, S. Takami, A. Okada, T. Mito, National
Institute for Fusion Science; Y. Matsubara, KEK; M.
Konno, Fuji Electric Systems Co.; A. Tomioka, Fuji
Electric Advanced Technology Co.; T. Imayoshi, H.
Hayashi, Kyusyu Electric Power Co..
The integrated current lead system, consists of a copper lead, a High
Temperature Superconductor and two stage pulse tube refrigerator,
has been developed for Superconducting Magnetic Energy Storage
(SMES) system. A two-stage pulse tube refrigerator, series connected
arrangement, was designed to satisfy the requirements for the
integrated current lead system. Operation of the first stage
refrigerator is four-valve method, while the second stage utilizes a
double inlet method. This arrangement ensures the compactness of
the current lead system. Refrigeration process of two-stage pulse tube
refrigerator has been investigated to validate the conceptual design
and finalize the current lead system development.
This work is supported by the NEDO under the contract of
"Superconducting Power Network Control Technology Development"
and by NIFS under ULAA114. The authors wish to acknowlege H.
Ohkubo at Suzuki Shokan Co. for his support.
C1-D-07 Damping of Intrinsic Temperature Oscillations
in a 4 K Pulse Tube Cooler
by Means of Rare Earth Plates
G. Thummes, L.M. Qiu, M. Dietrich, K. Allweins,
University of Giessen.
Regenerative cryocoolers, such as GM-coolers and pulse tube coolers,
show oscillations of the refrigeration temperature that result from the
periodic expansion of the working fluid (helium). In case of cryogenfree
operation of sensitive superconducting devices the temperature
oscillations can be rather disturbing because of the associated
variation of the critical current and gap voltage. The oscillations can
be damped by increasing the thermal mass attached to the cold end of
the cooler. For cooling near 4 K it is impractical to employ normal
metals for this purpose as in this case the specific heat of helium
greatly exceeds that of normal metals. Here we report on the damping
of temperature oscillations by making use of the high specific heat of
rare-earth alloys, such as ErNi. Tests were performed on two types of
in-house made 4 K pulse tube coolers with input powers of 6 kW and
1.7 kW. The damping is accomplished by ErNi-plates of different
thickness that were installed between the cold end of the 4 K stage
and the device mounting platform. E.g., with a 3.6 mm thick ErNiplate
(mass: 55 g) the temperature oscillation at 3.5 K was reduced by
a factor of 18 from 90 mK to 5 mK in the 1.7 kW-system. The thermal
resistance of the plate was 9 K/W, which was sufficiently low to
successfully operate an AC Josephson voltage standard near 4 K by
this set-up.
This work has been supported in part by the German BMBF (FKZ
13N8410). L.M. Qiu (permanent address: Zhejiang University,
Hangzhou 310027, P.R. China) thanks the DAAD for a fellowship.
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